Baked bread, a staple of the western world, is one of the oldest products manufactured from naturally occurring raw materials. Indeed, its basic ingredients, processes, and characteristics have changed little since the Stone Age.
Bread is made by mixing flour, water, salt, and yeast and kneading the mixture into a homogeneous mass which is then cooked or baked. Other ingredients are optional but greatly add to the character of the final product. One significant ingredient, wheat gluten, has traditionally been used as a protein additive in certain yeast-raised baked goods.
Wheat gluten is a complex mixture of proteins (75-80%), starch (15-20%), and fat (5-7%). The two main proteins are gliadin and glutenin. Gliadin gives gluten elasticity while glutenin gives it strength. Together, the proteins permit yeast-raised breads to maintain carbon dioxide gas produced during fermentation and thereby result in breads with a desired predetermined volume.
Gluten, however, has poor emulsifying activity and is largely insoluble in water at neutral pH. These characteristics have severely limited the use of gluten to a relatively small class of applications.
Various methods have been investigated and proposed to modify wheat gluten, including the production of a protein isolate from gluten by the removal of starch. These isolates, termed "wheat protein isolates" (W.P.I.), exhibit increased protein levels, 87-89% protein [N.times.5.7 dry basis].
These modification methods include attempts to increase gluten solubility in water by removing primary amides from glutamine and asparagine residues. In one process, wheat gluten is treated with alkaline chemicals at varying times and temperatures. The products have improved functional properties, but may also contain short chain peptides which, by their chemical nature and sequences, can impart a bitter taste to the modified gluten. Moreover, alkaline treatment saponifies the residual fats present in gluten, resulting in unpleasant soapy flavor and odor. Batey & Gras (1981) Journal Food Technology 16 561-566.
Another known process uses acids to effect full or partial deamidation of the side chains of gluten. Although some claim that these processes result in improved solubility, emulsification and whipping properties, the processes may also result in products which have unpleasant odors and bitter flavors, like those from alkaline modification processes.
Acid deamidation is also known to hydrolyze the wheat starch component of wheat gluten, a beneficial process that increases the concentration of functional protein content to a minimum 86%-87% protein [N.times.5.7 dry basis]. At the same time, however, acid deamidation exposes the fats in gluten to the rapid onset of oxidative rancidity. This effect makes the process commercially nonviable for food applications. J W Finley (1975) Journal Food Science 40 1283; Yagi et al (1985) European Patent No. 0164929.
Other attempts to modify gluten involve controlled enzyme hydrolysis by protease enzymes to achieve a range of solubilities and functionality. Enzymes can be from microbial, vegetable, or animal sources, and may be used under acid, neutral, or alkaline conditions.
Increased water solubility does generally result from most enzymatically modified glutens, but there is often a large reduction in molecular weight of the enzyme-hydrolysed glutens. In addition, the reaction products frequently contain low molecular weight peptides, including hydrophobic amino acids, which have an unpleasant bitter flavor.
Although some improvements in gluten functionality characteristics have been noted with these gluten modifications, such modifications are known to result in products which possess unacceptable flavor and odor. Indeed, artisans had produced and sold W.P.I. in the 1980's, but the W.P.I. exhibited such a level of undesirable fat rancidity that production was discontinued. Attempts to remove the offending fats were unsuccessful, likely due to the substantial bond between the fats and protein matrix. Thus, there remains in the art a need for a method to modify wheat gluten and to produce wheat protein isolates with satisfactory flavor and the desired functionality.